From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755733AbaHVBPv (ORCPT ); Thu, 21 Aug 2014 21:15:51 -0400 Received: from cn.fujitsu.com ([59.151.112.132]:31346 "EHLO heian.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1755714AbaHVBPt (ORCPT ); Thu, 21 Aug 2014 21:15:49 -0400 X-IronPort-AV: E=Sophos;i="5.04,376,1406563200"; d="scan'208";a="34921743" Message-ID: <53F698FD.6030409@cn.fujitsu.com> Date: Fri, 22 Aug 2014 09:12:29 +0800 From: Chai Wen User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:6.0) Gecko/20110812 Thunderbird/6.0 MIME-Version: 1.0 To: , Don Zickus CC: chai wen , Subject: Re: [PATCH] softlockup: make detector be aware of task switch of processes hogging cpu References: <20140821023051.GO49576@redhat.com> <1408599742-21674-1-git-send-email-chaiw.fnst@cn.fujitsu.com> In-Reply-To: <1408599742-21674-1-git-send-email-chaiw.fnst@cn.fujitsu.com> Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.167.226.161] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/21/2014 01:42 PM, chai wen wrote: > For now, soft lockup detector warns once for each case of process softlockup. > But the thread 'watchdog/n' may not always get the cpu at the time slot between > the task switch of two processes hogging that cpu to reset soft_watchdog_warn. > > An example would be two processes hogging the cpu. Process A causes the > softlockup warning and is killed manually by a user. Process B immediately > becomes the new process hogging the cpu preventing the softlockup code from > resetting the soft_watchdog_warn variable. > > This case is a false negative of "warn only once for a process", as there may > be a different process that is going to hog the cpu. Resolve this by > saving/checking the task pointer of the hogging process and use that to reset > soft_watchdog_warn too. > > Signed-off-by: chai wen > Signed-off-by: Don Zickus Hi Ingo & Don Ping... This patch is using the task pointer to check cases that softlockup can not reset itself, and has been tested. thanks chai wen > --- > kernel/watchdog.c | 16 +++++++++++++++- > 1 files changed, 15 insertions(+), 1 deletions(-) > > diff --git a/kernel/watchdog.c b/kernel/watchdog.c > index 0037db6..2e55620 100644 > --- a/kernel/watchdog.c > +++ b/kernel/watchdog.c > @@ -42,6 +42,7 @@ static DEFINE_PER_CPU(bool, softlockup_touch_sync); > static DEFINE_PER_CPU(bool, soft_watchdog_warn); > static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts); > static DEFINE_PER_CPU(unsigned long, soft_lockup_hrtimer_cnt); > +static DEFINE_PER_CPU(struct task_struct *, softlockup_task_ptr_saved); > #ifdef CONFIG_HARDLOCKUP_DETECTOR > static DEFINE_PER_CPU(bool, hard_watchdog_warn); > static DEFINE_PER_CPU(bool, watchdog_nmi_touch); > @@ -328,8 +329,20 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer) > return HRTIMER_RESTART; > > /* only warn once */ > - if (__this_cpu_read(soft_watchdog_warn) == true) > + if (__this_cpu_read(soft_watchdog_warn) == true) { > + /* > + * Handle the case where multiple processes are > + * causing softlockups but the duration is small > + * enough, the softlockup detector can not reset > + * itself in time. Use task pointers to detect this. > + */ > + if (__this_cpu_read(softlockup_task_ptr_saved) != > + current) { > + __this_cpu_write(soft_watchdog_warn, false); > + __touch_watchdog(); > + } > return HRTIMER_RESTART; > + } > > if (softlockup_all_cpu_backtrace) { > /* Prevent multiple soft-lockup reports if one cpu is already > @@ -345,6 +358,7 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer) > pr_emerg("BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n", > smp_processor_id(), duration, > current->comm, task_pid_nr(current)); > + __this_cpu_write(softlockup_task_ptr_saved, current); > print_modules(); > print_irqtrace_events(current); > if (regs) -- Regards Chai Wen